1. Field of the Invention
The present invention relates to a bias circuit providing different levels of bias power according to various power modes and a power amplifier having the same.
2. Description of the Related Art
In general, a power amplifier is a device supplying power to a load, and since it is positioned in a final stage of an amplifier circuit, it may also be referred to as a final stage amplifier.
It is important for a power amplifier to effectively supply power to a load without distortion, so a power transistor may be used as an amplifying element thereof.
Meanwhile, due to recent explosive growth in the wireless communications device market, large numbers of people can transmit and receive information through portable communications terminals, regardless of time and place. However, as large numbers of people are increasingly using wireless communications, diverse wireless services may be requested, and in order to meet the demand for diverse wireless services, portable terminals provide diverse applications; however, maximum talk time may be reduced.
The shortening of the maximum talk time is mainly due to power consumption and is caused by the limited battery capacity of portable terminals. However, an increase in battery capacity may lead to an increase in the volume of portable terminals, therefore failing to satisfy user demand for lighter, thinner, shorter, and smaller portable terminals. Thus, portable terminal battery power is required to be used effectively.
The foregoing power amplifier may also be employed in a portable terminal to be used for wireless communications and may be used to amplify the power of a transmitted and received signal. Thus, in order to use the battery power of a portable terminal effectively, the power amplifier is also required to use power effectively. Thus, a power amplifier may selectively operate in either a high power mode or a low power mode.
A power amplifier receives bias power in order to perform an amplifying operation. In general, a power amplifier receives the same amount of bias power while operating in both the high power mode and the low power mode, causing a problem in which power usage is ineffective.
In order to solve the foregoing problem, a technique of supplying different levels of bias power according to various power modes has been disclosed in the related art document, but in this technique, a separate bias circuit is provided for each power mode, thereby increasing a circuit area and thus causing a further problem in which the volume of a portable terminal is increased.